How You Digest Carbs May Influence Weight Gain, Study Says

Researchers focused on a gene called AMY1, which is responsible for an enzyme in the saliva called salivary amylase. When food enters the mouth, the enzyme begins the process of starch absorption that continues in the digestive system. Starches are a type of carbohydrate.

People typically have two copies of AMY1, but the number of copies can vary widely. It's believed that higher numbers of the gene evolved in response to diets that contained greater levels of starch, the researchers said.

They studied the number of copies of AMY1 in thousands of people from France, Singapore, Sweden and the United Kingdom, and found those with a low number of copies were more likely to be obese.

People with fewer than four copies of the gene were about eight times more likely to be obese than those with nine copies. For every additional copy of the gene, a person was about 20 percent less likely to be obese, according to the authors of the study published March 30 in Nature Genetics.

"I think this is an important discovery because it suggests that how we digest starch and how the end products from the digestion of complex carbohydrates behave in the gut could be important factors in the risk of obesity," study co-lead author Dr. Philippe Froguel, chair of genomic medicine at the School of Public Health of Imperial College London, said in a college news release.

"Future research is needed to understand whether or not altering the digestion of starchy food might improve someone's ability to lose weight, or prevent a person from becoming obese," Froguel said.

"We are also interested in whether there is a link between this genetic variation and people's risk of other metabolic disorders such as diabetes, as people with a low number of copies of the salivary amylase gene may also be glucose intolerant," Froguel said.

Previous studies investigating obesity have identified variations in genes that act in the brain and often result in differences in appetite, study first author Dr. Mario Falchi, also from Imperial College London, said in the news release. "Our finding is related to how the body physically handles digestion of carbohydrates."

Falchi said researchers are starting to develop a clearer picture of a combination of genetic factors that contribute to a person's chances of becoming obese. "This should ultimately help us to find better ways of tackling obesity," he said.

More information

The U.S. National Institute of Diabetes and Digestive and Kidney Diseases has more about overweight and obesity.